Interpretive Summary: Increasing demand for food and agricultural products directly relates to increased greenhouse gas (GHG) emissions, particularly for the three primary gases associated with agriculture [nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)]. The atmospheric concentrations of these gases have increased significantly and are projected to continue to do so according to the report by the Intergovernmental Panel on Climate Change (IPCC). According to US EPA, total GHG emission for the United States in 2004 was estimated as 84.6% from CO2, 7.9% from CH4, 5.5% from N2O and 2% from other sources. Nitrogen (N) is one of the most important nutrients required for the survival of all living organisms and it is ubiquitous in the environment. Commercial N fertilizers and organic N sources such as animal manure stimulate N losses mainly in the form of N2O and volatilization through biochemical processes. Commercially available enhanced-efficiency N fertilizers such as those containing nitrification inhibitors, urease inhibitors, and slow-release fertilizers can potentially increase the N-use efficiency by crops and reduce N losses. Our objective was to quantify N2O, CH4, and CO2 emissions from application of several commonly used inorganic N fertilizers, commercially available enhanced-efficiency N fertilizer, and poultry litter under no-till corn production. No significant differences were observed in N2O emissions among the enhanced-efficiency N fertilizers and other N fertilizer sources. The CH4-C and CO2-C emissions were impacted by the environmental factors more than the N source. Results demonstrated that N fertilizer source and climate conditions need consideration when selecting N fertilizer that reduces GHG emissions.

Technical Abstract:
There is a growing interest in the quantification of significant sources of greenhouse gas (GHG) emissions from agricultural practices. Alternative N fertilizers that produce low GHG emissions from soil are needed to reduce the impact of agricultural practices on global warming potential (GWP). We quantified and compared growing season fluxes of N2O, CH4, and CO2 resulting from applications of different N fertilizer sources, urea-ammonium nitrate (UAN), ammonium nitrate (NH4NO3), poultry litter, and commercially available enhanced-efficiency N fertilizers as follow: polymer-coated urea (ESN®), superU®, UAN + AgrotainPlus® (urease inhibitor), and poultry litter + AgrotainPlus in a no-till corn (Zea mays L.) production. Greenhouse gas fluxes were measured during two growing seasons using static, vented chambers. The enhanced-efficiency N fertilizer ESN delayed the N2O flux peak by 3 to 4 weeks compared to other N sources. No significant differences were observed in N2O emissions among the enhanced-efficiency N fertilizers and other N fertilizer sources. Cumulative growing season N2O emission from poultry litter was significantly greater than from inorganic N sources. The N2O loss (2-y average) as a percentage of N applied as fertilizer was 0.69% for superU, 0.98% for UAN, 2.0% for ESN, 0.8% for urea, 1.7% for NH4NO3, and 4.5% for poultry litter.
The CH4-C and CO2-C emissions were impacted by the environmental factors more than the N source. The cumulative growing season CO2 fluxes were less variable than CH4, however, no significant difference or trend was observed among N sources. These results demonstrate that N fertilizer source and climate conditions need consideration when selecting N fertilizer that reduces GHG emissions.